1) Field of the Invention
The present invention relates to an apparatus and a method of forming an image on both sides of a recording medium.
2) Description of the Related Art
Image forming apparatuses like a copier, a printer, a facsimile and the like are made to form an image on both surfaces of a recording medium (hereinafter, “paper”). In a conventional image forming apparatus capable of recording on both surfaces of a paper, an image (visualized image) of one of the surfaces formed on an image carrier is transferred and fixed onto one surface (front surface) of the paper. The paper is then turned over by an arrangement, such as a passage, re-fed, and an image (visualized image) of the other surface formed on the image carrier is transferred and fixed on to the other surface (reverse surface) of the paper. This has been a prevalent method.
However, the recording on both surfaces by this method has left several issues concerning the reliability of paper transfer attributed to curling of a paper caused by fixing of an image on one surface and changing the transfer direction of paper.
In this context, Japanese Patent Application Laid-Open Publication No.1989-209470 discloses a method of fixing an image in one stroke after transferring a toner image on both surfaces of a paper using a first image carrier and a second image carrier.
According to this publication, a 1st image formed on a photoreceptor is transferred to a transfer belt by a first transfer device and a 2nd image formed on a photoreceptor is transferred directly onto one surface of the paper by the first transfer device. The 1st image is then transferred onto the other surface of the paper by a second transfer device, thereby achieving transfer of the images onto both the surfaces of the paper. This paper is then carried to a fixing unit for fixing the images.
However, according to the method published in this publication, the transfer belt is turned twice for recording on both surfaces of the paper. With this method there is a drawback that, productivity during continuous printing is declined, as the image formation starts after completion of one full turn of the transfer belt, before starting formation of the 2nd image.